This invention relates to a timing apparatus, and in particular to a timing apparatus for activating a plurality of electrical loads at predetermined time intervals in blasting operations.
During mining and quarrying operations, it is necessary to detonate a series of explosive charges in an accurately timed sequence to achieve the correct blast pattern. In the past, the most common way of achieving this has been to use a train of pyrotechnic delay fuses and ignitor cord to link up detonators. In recent years however, systems for generating a controlled sequence of electrical timing signals have been introduced (see, for instance, U.S. Pat. Nos. 2,546,686 and 3,212,869, and South African Patent No. 79/0355).
In South African Patent No. 79/0355, a system is described in which a central control unit programmes a plurality of remote delay devices with corresponding reference timing signals via an electrical cable line and subsequently activates the detonators to which the delay devices are attached.
Rockfalls and explosions elsewhere in the mine can damage both the remote delay devices and the electrical harness line interlinking these devices and the control unit. If this occurs before or during programming, then it becomes necessary to abort the blasting operation, as some of the delay devices have not been provided with their reference timing signals, and cannot be subsequently triggered.
Electrical failure or malfunctions in the central control unit or in the remote delay devices may also lead to serious accidents.
As a mine is generally evacuated during blasting, the down-time wasted as a result of such malfunctions occuring is extremely costly.